Generally, in a Package on Package (PoP) system individual semiconductor dies may be packaged either separately (or with multiple semiconductor dies in each separate package), and then the separate packages may be brought together and interconnected so that the individual semiconductor dies in the separate packages may be integrated together in order to perform a desired tasks. The individual packages may be electrically interconnected to each other, for example, by using contact bumps.
Such contact bumps may be formed by initially forming a layer of the contact material onto a substrate of the package. Once the layer of the contact material has been formed, the layer of contact material may be reflowed, by which the temperature of the contact material is increased in order to at least partially liquefy the contact material. This partial liquefaction allows the contact material to pull itself into a ball shape using its own surface tension.
Once formed, the contact bumps of one package may be placed into contact with contact pads from another package. Alternatively, the contact bumps may be placed into contact with other types or forms of contacts formed on the other package. Once the contact bumps have been aligned with their appropriate locations, the contact bumps may again be reflowed and reheated in order to again partially liquefy them and cause them to partially flow and form a bridge between the two packages. Once the contact bumps cool down and resolidify, the contact bumps are fully joined to each other. This joint between the contact bumps allows for both a physical connection between the contact bumps as well as an electrical connection that allows signals and power to cross from one package to another, thereby allowing the two packages to be integrated with each other and work together.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.